Infectious Diseases

PCR tests

Question:

I`ve researched and read that PCR tests are extremely accurate and reliable. How sensitive and specific are these tests when testing cerebral spinal fluid (due to meningitis-like symptoms)for HSV?

Answer:

Two Large Studies Have Addressed your Question Using as Gold Standard Brain Biopsy: 1. Lakeman FD, Whitley RJ. Diagnosis of herpes simplex encephalitis: application of polymerase chain reaction to cerebrospinal fluid from brain-biopsied patients and correlation with disease. National Institute of Allergy and Infectious Diseases Collaborative Antiviral Study Group. J Infect Dis 1995; 171:857-63. 2. Aurelius E, Johansson B, Skoldenberg B, Staland A, Forsgren M. Rapid diagnosis of herpes simplex encephalitis by nested polymerase chain reaction assay of cerebrospinal fluid. Lancet 1991; 337:189-92. Both Studies Report Sensitivities Near 98% and Specificity of 94%. The major Drawbacks of PCR testing for Herpes encephalitis and meningitis is the lack of standardization: No test has been approved by the FDA, so each Lab performs its own `home brew` version of the test, which may or may not perform as well as the tests validated in the literature. Another practical problem of this tests is the turnaround time. Given the current environment of merging and cost containment, Rarely does the Local Hospital Laboratory perform the test on site. Rather, the samples are sent to big national reference labs, given a realistic 6 to 10 days delay in the test result reports. By this time, the decision to treat or not to treat for Herpes encephalitis or meningitis is probably made on clinical grounds. Also it is germane to consider that patients CSF may contain inhibitors of the PCR reaction, which could result in false negative results.

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